Russia fired 30 cruise missiles into the Yavoriv military base at 5.45am, the day after Putin warned the West that convoys carrying weapons from NATO would be legitimate targets.
The attack just six miles from NATO member Poland was a terrifying step change that brought the West closer to a military confrontation with Moscow.
Russian opposition politician Leonid Volkov, ex-chief of staff for jailed Kremlin critic Alexei Navalny, warned Putin was “crazy enough” now to use nuclear weapons.
He told Sky News' Sophy Ridge on Sunday: “It is now very clear that enormous cost has to be paid to stop this war.
"There are all the sanctions, creating a burden on the European economy. But this cost has to be paid because otherwise, Putin will just destroy the world.”
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And Poland’s President Andrzej Duda said he feared Putin would resort to using chemical weapons.
He said: “I think that Putin can use anything right now, especially because he’s in a very difficult situation. If he used weapons of mass destruction this would be a game-changer.”
The Yavoriv International Peacekeeping and Security Centre in the Lviv region has been used by foreign instructors, including ex-military from the UK, to train Ukrainians.
So far, no British casualties have been reported to the UK authorities from the Lviv region airstrikes.
The Yavoriv base is central to Putin’s paranoia about NATO moving closer to Russia and the attack ramped up tensions between Moscow and the West.
The ex- Ukrainian national security chief Oleksandr Danylyuk said: “Because Russia obviously miscalculated the reaction of Ukrainians and the West they can start some provocations in NATO countries, probably Estonia, Latvia and Lithuania, very soon.”
Mr Danylyuk said the attack on the Yavoriv base was “a very clear message” that Moscow was ready to attack NATO troops supplying weapons to Ukraine.
After the attack, 19 ambulances and fire fighting teams were seen rushing to the base. Many wounded foreigners were taken across the border to Poland for treatment.
Speaking about the close proximity of the base to Poland, Markiyan Lubkivsky, an adviser to the Ukrainian defence minister, said: “This is very close. Nobody can be safe. It was a terrible attack.
“So the geography of Putin’s attack is becoming wider.”
In Ivano-Frankivsk, air raid sirens went off at 3.30am, sending people into bomb shelters, where they stayed for three hours before the all-clear sounded.
But shortly after, at 6.30am, a massive explosion was heard throughout the city and a large column of black smoke rose from above Ivano-Frankivsk airport.
Mayor Ruslan Martsinkiv confirmed Russian forces had hit the airport, but there were no casualties.
Shortly after the attack, Mr Martsinkiv warned residents: “Keep at home for your safety.
“When the danger passes I will let you know.”
On Sunday afternoon Ukrainian fighter jets patrolled the skies over Ivano-Frankivsk, for fear of long-range attacks by the Russians.
Local security teams have been trying to track down Russian saboteurs feared to be in the city.
Soldiers at the airport, which has now been hit three times, stopped the Mirror from approaching the bomb site, one of them telling us politely: “We must ask you not to come back here again.”
Asked if the airport had been badly hit, he smiled and said: “I must ask you to go away and do not come back.”
Peace talks between Russia and Ukraine continue today as US and Chinese officials meet in Rome amid growing tension over the war.
In his Sunday blessing in St Peter’s Square, Pope Francis said the killing of children and civilians was “barbaric”.
He called besieged Mariupol a “martyred city” and appealed for “truly secure humanitarian corridors” to let people flee.
He said: “Stop this unacceptable armed aggression before it reduces cities into cemeteries.”
